1. Field of the Invention
The present invention generally relates to a supporting structure for exhaust pipes. More particularly, the invention relates to a supporting structure for exhaust pipes such as in a vehicle, of the type with which an exhaust pipe drawn out from an engine is supported at the side of a vehicle body through an elastic member.
2. Description of Relevant Art
In general, the exhaust pipe, which is drawn out from an engine installed in a vehicle, is supported at the side of a body of the vehicle through an elastic member.
In the accompanying drawings, FIG. 5 is a schematic side view exemplarily showing such supporting structure for exhaust pipes.
In this exhaust pipe supporting structure, a flexible tube 56, which constitutes a substantially intermediate part of an exhaust pipe 52 drawn out from an engine 51 mounted at the side of a body (not shown) of a vehicle, is supported at the side of a frame 54 of the vehicle body through an elastic member 53 as an anti-vibratory member, with an intention to thereby prevent the transmission of vibrations from the exhaust pipe 52 to the side of the vehicle body, while restricting the displacement of the exhaust pipe 52.
The engine 51 is of a horizontal type disposed in the front part of the vehicle, and the exhaust pipe 52 is extended therefrom once downwardly and then substantially horizontally in the longitudinal direction of the vehicle.
Detailed description will now be made of this exhaust pipe supporting structure.
The elastic member 53 is of a circular form elongated in the vertical direction in side view, and has a uniform thickness t (see FIG. 6) in the transverse direction of the vehicle.
At the upper part of the elastic member 53, there is inserted therethrough an extension 55a as a bent part of a stay 55 which is fixed to the body frame 54 and extended in the rearward direction of the vehicle, whereby the elastic member 53 is supported at the vehicle body side.
Further, from a flange 57 at the rear end of the flexible tube 56 is standing a bracket 58 in the frontward direction of the vehicle. The bracket 58 has at the front end thereof a pin 58a projected therefrom in the transverse direction of the vehicle. The pin 58a is inserted into the lower part of the elastic member 53, whereby the exhaust pipe 52 is supported at the vehicle body side through the member 53.
Incidentally, in FIG. 5, designated at reference numeral 60 is a slot punched to be opened, in the form of a letter "H" in side view, through the vertically central part of the elastic member 53, in the thickness direction thereof.
Moreover, as shown in FIG. 5, a line segment L.sub.6 passing a connection point 55a at the vehicle body side of the elastic member 53 and the pin 58a as another connection point thereof at the side of the exhaust pipe 52 is set to be substantially vertical, in side view.
On the elastic member 53 arranged like this, there are acting, as shown in FIG. 6 which is a sectional view along line VI--VI of FIG. 5, forces (collectively designated by reference character F.sub.1 ') in the tension/compression direction of the member 53 as well as forces (likewise designated by reference character F.sub.2 ') in the shearing direction thereof. Further, in cases where the forces F.sub.1 ', F.sub.2 ' are caused to concurrently act on the elastic member 53, there are resulted such forces (likewise designated by reference character F.sub.3 ') that act on the member 53 with a tendency to rotate the elastic member in either direction of rotation about the connection point 55a as a supporting point thereof at the vehicle body side.
In this concern, in FIGS. 4A and 4B, designated at C.sub.6, C.sub.7 are characteristic curves showing, for a case where the thickness t of the elastic member 53 is relatively small, those relations to be observed, in the tension/compression direction and the shearing direction of the member 53, respectively, between various values, in terms of kg, of the forces F.sub.1 ', F.sub.2 ' acting on the member 53 and displacements D, in terms of mm, by corresponding deformations of the member 53.
As will be comprehended, the elastic member 53 is not well adapted for effective exhibition of restraint against the respective external forces F.sub.1 ', F.sub.2 '.
In view of such characteristic of the elastic member 53, the restraint by the member 53 against the force F.sub.1 ' in the tension/compression direction thereof might well be raised by employing such an elastic member as one higher in spring coefficient or spring rate than the member 53 but similar thereto in configuration and size, including thickness. But, in this case, it would be hardly possible to raise the restraint against the force F.sub.2 ' in the shearing direction of the elastic member 53.
On the other hand, by way of such a modification that the thickness t of the elastic member 53 be increased, the restraint against the force F.sub.2 ' in the shearing direction of the member 53 might well be raised as shown by curve C.sub.9 of FIG. 4B. In this case, however, the restraint against the force F.sub.1 ' in the tension/compression direction of the elastic member 53 would be excessively raised as shown by curve C.sub.8 of FIG. 4A, in addition to corresponding increase in the quantity of rubber to be used as such elastic member, as well as in cost.
In this respect, in Japanese Utility Model Lay-Open Print No. 55-94225 laid open on June 30, 1980, there is disclosed a different type of elastic member as an anti-vibratory member to be used in an exhaust pipe supporting structure for vehicles.
In the accompanying drawings, FIGS. 7 and 8 are a side and a sectional views of an elastic member 100 of the disclosed type.
The elastic member 100 is gradually enlarged in thickness along its length from the upper part to the lower part thereof, with an intention to thereby make uniform the respective deformations at various points along the length of the member 100, when it is subjected to forces acting in the tension/compression direction and the shearing direction thereof.
However, the restraint by the elastic member 100 is not yet sufficiently effective against such forces that act on the member 100, in the rotating direction, like the force F.sub.3 ' acting on the member 53.
Referring again to FIG. 5, designated at reference character Tr is a torque roll axis adapted to serve as a center axis of vibrations of the engine 51 when the vehicle is accelerated or decelerated. In accordance with horizontal arrangement of the engine 51, the torque roll axis Tr is set so as to extend in the transverse direction of the vehicle.
The vertical line segment L.sub.6, on which the connection points 55a, 58a of the elastic member 53 are located as described, is designed so as to cross, in side view, an imaginary arc 64 as a part of such a circle about the torque roll axis Tr that passes the center of gravity of the member 53.
In other words, the two connecting points 55a, 58a of the elastic member 53 will not be both found on any imaginary arc of an arbitrary radius that has the center thereof on the torque roll axis Tr.
Accordingly, no vibrating forces on the exhaust pipe 52 due to engine vibrations about the torque roll axis Tr will substantially act as a force on the elastic member 53 in the tension/compression direction thereof. Against such engine vibrations, therefore, the restraint by the elastic member 53 is low, thus resulting in the difficulty of effectively reducing the engine vibration by use of the afore-mentioned exhaust pipe supporting structure. Besides, if managed to be adapted for such reduction, this supporting structure would be complicated in constitution and would be expensive.
Incidentally, the above comments on the torque roll axis Tr applies also to one I of the principal axes of inertia of the engine 51 that extends in the same direction as the torque roll axis Tr and functions as a principal center axis of vibrations of the engine 51 while the vehicle is not accelerated or decelerated. Though, generally, depending on the engine structure, the principal axis I and the torque roll axis Tr are coincident with each other in the example shown.
Such problems in conventional exhaust pipe supporting structures of the type described are particularly remarkable in an FF (front-engine, front-drive) type vehicle with an engine arranged horizontal, in which, in plan view, an exhaust pipe is rearwardly directed to be perpendicular to a torque roll axis of the engine or to such principal axis of inertia thereof as extending in the same direction as the torque roll axis, so that an exhaust system is greatly affected by engine vibrations about the torque roll axis or the principal axis of inertia.
The present invention has been achieved to effectively solve such problems in conventional exhaust pipe supporting structures of the type described.